1. Field of the Invention
The present invention relates to a method for coating an anti-reflection film, on the surface of an optical material and more particularly to a method for a vacuum-depositing, on the surface of a transparent optical material of glass or synthetic resin, silicon oxide SiO and silicon dioxide SiO.sub.2 whose refractive indices are varied by changing the conditions of the vacuum-deposition, under a predetermined condition of the vacuum-deposition so as to form a firm and durable anti-reflection film.
2. Description of the Prior Art
It is well-known to coat an anti-reflection film on a transparent optical material (hereafter referred to as "substrate" for brevity) through a vacuum-deposition method. For example, a single film of MgF.sub.2 was vacuum-deposited as an anti-reflection film on the surface of a substrate. According to the conventional vacuum-deposition method, however, unless the surface of the substrate is cleaned and heated up to temperatures of 150.degree.-350.degree. C. in vacuum to completely remove moisture and organic contamination on the surface, a satisfactory anti-reflection film cannot be formed or the resultant anti-reflection film, even if formed satisfactory fortunately, is very lacking in durability. Moreover, the conventional method is by no means considered satisfactory due to the fact that the heating of the substrate up to temperatures higher than 150.degree. C. usually accompanies a change in the material, and physical deformation and degradation in light transmittivity in the case where a synthetic resin substrate or polarizing substrate of glass layers with a high-molecular film interposed therebetween is used.